The present invention relates to a magnetic memory medium having a three-dimensional structure aiming super high density of information memorized in a magnetic bubble memory device and a method for setting an initial state of the magnetic memory medium.
In general, in an outside memory equipment of a large computer system which utilizes a magnetic bubble memory device, signals (magnetic bubbles) are transferred along a transfer pattern by applying an in-plane magnetic field, so that a high reliability of memorization is realized due to the fact that the number of the mechanically driven elements is small and the bubble is non-volatile. However, in these days, the magnetic bubble memory medium has been required to memorize information in higher density than before and to reduce the access time to process data in higher speed than before. In order to achieve the requirement of realizing a magnetic bubble memory medium of high memory density, it is necessary to form each magnetic bubble diameter in a very small size such as in a submicron dimension (less than 1 .mu.m) and arrange fine transfer patterns in high density in order to match with the minute magnetic bubble. However, the bubble transfer margin is reduced and the access time is prolonged according as the bubble diameter becomes small. Therefore, the high density arrangement of the magnetic bubbles in a plane is limited.